1. Technical Field of the Invention
The present invention relates to a biometric sensor apparatus and method. More particularly, but not exclusively, it relates to a biometric sensor apparatus and method for determining blood volume variations with respect to time in a body part. Even more particularly, the invention relates to an apparatus and method for determining blood volume variations with respect to time in a body part to identify and measure features of a user's heart beat.
2. Description of Related Art
The field of biometrics relates to the statistical analysis of physiological characteristics. For the purposes of identification for security or other purposes, features such as finger prints or retinal scans can be used to uniquely identify individuals.
A weakness of many biometric systems is that they can be fooled or “spoofed”. In the case of a fingerprint reader this is done by copying or lifting a fingerprint of a legitimate individual from a surface such as a drinking glass and subsequently presenting it to a fingerprint reader to impersonate that person.
For example, every person has a unique set of fingerprints, and this provides a basis for identification. An image of a fingerprint can be taken and analyzed to see if it matches a recorded sample of the user's fingerprints. This is done by analyzing a number of details, or “minutiae” of the fingerprint. The greater the number of minutiae that are matched, the less the chance of incorrectly identifying an individual.
However, a biometric identification system that relies solely on mathematical analysis of simple optical images can be easily spoofed, as a copy of the pattern of a fingerprint can be easily made and presented to a reader device.
Systems have been developed to determine whether a sample used in a biometric identification process is from a living person i.e. a live finger, or a photocopy, synthetic model or suchlike.
European Patent application publication number 1353292A (the disclosure of which is hereby incorporated by reference) describes the use of visible and/or infra red (IR) illumination to capture an optical image of the blood vessels of a user's finger. These images show a changes in opacity of the blood vessels due to blood flow. The changes in opacity of the blood vessels of a user's finger during the cardiac cycle can be used to infer the user's liveness (i.e., that the presented finger is from a live person, rather than some inanimate copy). This enables the system to distinguish a biometric sample presented to a fingerprint reader from a living user to that from a fake finger or spoof.
Typically, heart rate monitors work on the same principal as a two lead ECG and signals are acquired using electrical detectors fitted into a chest strap. These detectors record instantaneous heart rate, maximum heart rate, average heart rate over a period and/or exercise time in a heart rate zone.
As used herein, “an optical image sensor” means a sensor that is responsive to electromagnetic radiation at least in the visible and/or infra red (IR) or near-IR regions. Hereafter, references to IR include near-IR, for example 700 to 1100 nm (nanometers).